1. Field of the Invention
The present invention relates to a cement clinker grinding apparatus using a vertical roller mill and a method of grinding cement clinkers by the same apparatus, by which cement clinkers are ground and produced as cement products by use of a vertical roller mill.
2. Description of the Related Art
FIG. 5 shows a related art cement clinker grinding apparatus using a vertical roller mill.
In FIG. 5, a separator built-in type vertical roller mill 1 is used for grinding cement clinkers. In the vertical roller mill 1, a table 3 rotatable around a vertical axis 2a is disposed in a housing 2. The table 3 is rotated by a motor 4. Further, a plurality of rollers 5 are arranged on the table 3 so as to be pressed against the table. Further, a built-in separator 6 is arranged over the table 3. Feed material 7 supplied from above the built-in separator 6 is ground between the rollers 5 and the table 3. The ground material is blown or air swept in the upward direction by cool air 8 introduced into the housing 2 from under the table 3, and then classified by the built-in separator 6 into some classes according to the particle diameters of the cement products. The coarse powder having large particle diameters are returned again onto the table 3 within the housing 2. Further, some large particles of diameter which cannot be blown up by the cool air 8 is discharged from under the table 3 and, conveyed upward by a bucket elevator 9, and then returned onto the table 3 together with the newly feed material 7. The fine powder for the products separated by the built-in separator 6 is conveyed to a product collector 10 provided with a bag filter, for instance. The product collector 10 can separate the fine powder from air. The cool air 8 introduced into the separator built-in type roller mill 1 is generated by a suction force of a suction fan 11 provided on the outlet side of the product collector 10.
In the related art cement clinker grinding apparatus using the separator built-in type roller mill 1 as described above with reference to FIG. 5, in order to classify the cement products by the built-in separator 6 provided at the upper portion of the housing 2, it is necessary to introduce a large amount of cool air 8 from under the table 3 so that the particulate material ground between the table 3 and the rollers 5 can be blown up for air flow conveyance. Therefore, the pressure loss within the vertical roller mill is relatively large, and further the power consumption of the suction fan 11 is also very large.
In addition, in the products produced by use the vertical roller mill 1, there exists such a tendency that the particle size distribution of the products is narrow, so that the quality of the cement products deteriorates, in comparison with the products produced by a tube mill as disclosed in Japanese Published Unexamined Patent Application No. 5-111643,
Further, in the related art separator built-in type vertical roller mill 1, since the ground material are air-swept in the upward direction to the built-in separator 6 arranged on the upper side of the housing 2 for air flow conveyance, the structure of the vertical roller mill 1 is so constructed in such a way that a large amount of cool air 8 can be introduced. Therefore, since the amount of air to be introduced into the vertical roller mill 1 is large and thereby the cooling performance is large, the temperature of the ground material is relatively low. As a result, a problem arises in that there exists a possibility of false cement setting due to the crystallization water of gypsum. Therefore, in order to prevent the false cement setting, an installation for introducing hot air from the outside is additionally required, thus causing another problem in that the installation cost is high.